With growing pressure to reduce pesticide use, fruit growers require an alternative to herbicidal control of weeds. One option is the use of mulches or permanent vegetative ground covers, which in turn may have advantages in promoting soil physical properties and improving growth. This study examined the short-term effects of ground cover management in two newly established dwarf apple orchards in Quebec. Effects of cultivation, composted manure mulch, straw mulch, grass cover crops, a cover crop mixture of lupin and wild carrot (mixed flora) and geotextile were determined, comparing soil aggregate stability, bulk density, temperature, volumetric water content and tree growth. Straw and geotextile mulches resulted in higher soil water contents and tree growth relative to soil under grass or mixed flora ground cover. Ground cover maintained soil aggregate stability. Soil temperatures were highest under cultivation and geotextile treatments in spring and summer months, and apple yields and growth rates were greater than for ground cover treatments. Straw mulch buffered soil from temperature variation. Little effect of mulch treatments on soil bulk density was observed. Given that soil water content was the primary factor related to optimum orchard production straw and geotextile mulches promoted soil water retention and could be considered superior management options for growers, depending on costs of establishment and maintenance of the mulches. Key words: Mulches, ground cover, bulk density, aggregate stability, soil temperature, volumetric water content

tion in both plantlets (33 -56% relative increase) and plants Changes in LT 50 and carbohydrate levels in response to cold acclimation were monitored in vitro and in vivo in red rasp-(143 -191% relative increase). Sucrose increased 124-165% in plantlets and 253 -582% in container-grown plants during berry (Rubus idaeus L.) cultivars with different levels of cold hardiness. Entire micropropagated plantlets or shoot tips from acclimation and declined rapidly to the level of control plants during deacclimation. Glucose and fructose also accu-3 cultivars were harvested before, during and after cold acclimation. Cane samples from container-grown plants of 4 culti-mulated, but to a lesser extent than sucrose. Raffinose concentrations were very low, but increased significantly vars were harvested before and during cold acclimation and deacclimation. Samples were evaluated for cold hardiness during cold acclimation. In vitro, genotype hardiness was related to the high concentrations of total soluble carbohy-(LT 50 ) by controlled freezing, then analyzed for carbohydrates, including starch, sucrose, glucose, fructose and drates, sucrose and raffinose. In vivo, hardier genotypes had raffinose. Hardiness of cold-acclimated 'Muskoka' and 'Festi-lower concentrations of starch than the less hardy genotypes. These results demonstrated the importance of soluble carbohy-val' was superior to that of 'Titan' or 'Willamette'. In vitro drates, especially sucrose, in cold hardening of red raspberry plantlets had higher levels of soluble carbohydrates on a dry weight basis and higher ratios of sucrose:(glucose +fructose) and that the in vitro conditions or controlled acclimation than the container-grown plants. Total soluble carbohy-conditions do not necessarily reflect the phenomena observed in vivo. drates, primarily sucrose, accumulated during cold acclima-Of the soluble carbohydrates, high relative sucrose levels are most often associated with increased cold hardiness (Levitt 1980, Kandler andHopf 1982). This was observed in cloudberry (R. chamaemorus L.; Kaurin et al. 1981) and raspberry (Palonen 1999). Relative concentrations of the raffinose family oligosaccharides (RFO) (raffinose and stachyose), but not other sugars, are positively correlated with season-long cold hardiness in several species, including red currant (Ribes sati6um Rchb. Syme), western sandcherry (P. besseyi Bailey), grape (Vitis riparia × labrusca 'Valiant') (Stushnoff et al. 1993), red osier dogwood (Cornus sericea L.) (Ashworth et al. 1993, Stushnoff et al. 1993), 3 Forsythia taxa (Flinn and Ashworth 1995 and Lonicera caerulea L.

This article gives an overview of the current state of cold hardiness research in fruit crops by reviewing the recently published studies on cold hardiness of both tree fruit and berry crops. Topics discussed include cold hardiness of fruit species, cultivars and different plant organs, biophysical and biochemical aspects of hardiness, evaluation of hardiness, as well as endogenous, cultural and environmental factors affecting cold hardiness in these species. Lack of cold hardiness is a major limiting factor for production of fruit crops in many regions of the world and improved cold hardiness one of the major objectives in numerous breeding programs and research projects. Screening cultivars or selections for cold hardiness is commonly done, and different methods applied to the evaluation of hardiness are discussed. The physical limit of deep supercooling may be a restricting factor for expanding the production of some fruit crops, such as Prunus species and pear. As for biochemical aspects, a relationship between carbohydrates and cold hardiness is most commonly found. Studies have also been made on different hardiness modifying cultural factors including rootstock, crop load, raised beds and application of growth regulators. The latter seems promising for some species. Cold hardiness is an extremely complex phenomenon and understanding different mechanisms involved is critical. Since hardiness is, however, primarily affected by genotype, developing cold-hardy fruit cultivars and effective screening methods for hardiness are essential. Finally, cultural practices may be improved to further enhance hardiness. Key words: Berries, cold hardiness, fruits, small fruits, stress, winter hardiness

Three methods (Kjeldahl, sulfuric acid-hydrogen peroxide, and summation of amino acid content) for determining and calculating the protein content of apple flower buds were compared. Quantitation of protein content based on summation of amino acids appears to be the most accurate method. A new nitrogen:protein conversion factor (5.51) was calculated based on total amino acid analysis. This new conversion factor could replace the conventional 6.25 factor for estimating total protein content of apple flower bud by the Kjeldahl method. However, Kjeldahl is not an accurate method for estimating protein content in apple flower bud tissue, regardless of the conversion factor, and probably would not be a good method for estimation of protein in other plant species.

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